Multi-engine aircraft thrust balancing

ABSTRACT

An aircraft controller includes a memory for storing instructions. The instructions are operable to cause the controller to perform a thrust balancing method and ensure a balanced thrust output from the aircraft. The thrust balancing method includes comparing an aircraft control surface setting in a cruise flight mode with the aircraft control surface setting in a flight idle mode of operations, thereby isolating an asymmetric thrust component of the aircraft control surface settings and determining an asymmetric thrust bias based on the isolated asymmetric thrust component of the aircraft control surface settings.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.61/870,806 filed on Aug. 28, 2013.

TECHNICAL FIELD

The present disclosure relates generally to multi-engine aircraft, andmore particularly to a thrust balancing system for the same.

BACKGROUND OF THE INVENTION

Multi-engine aircraft, such as passenger jets, operate in multiple modesduring any given flight, with the majority of the flight spent in acruise mode. Because of uneven wear and/or uneven age of the aircraftengines, the actual thrust output of each of the engines can vary evenwhen conventional thrust metrics such as Engine Pressure Ratio (EPR) andLow Rotor Speed (N1) indicate approximately identical thrust outputs.

During cruise mode, if the multiple engines are outputting uneven(non-symmetrical) thrust, aircraft control surfaces are used to maintaina correct aircraft heading, and ensure that the aircraft does not go offcourse. Continuously operating the aircraft with asymmetric thrust andaircraft control surface corrections results in a decrease in fuelefficiency of the aircraft and an increase in the fuel costs for anygiven flight.

SUMMARY OF THE INVENTION

An aircraft controller according to an embodiment of this disclosure,among other possible things includes a non-transient storage medium, thenon transient storage medium storing instructions operable to cause thecontroller to perform the steps of, comparing an aircraft controlsurface setting in a cruise flight mode with the aircraft controlsurface setting in a flight idle mode of operations, thereby isolatingan asymmetric thrust component of the aircraft surface settings, anddetermining an asymmetric thrust bias based on the isolated asymmetricthrust component of the aircraft surface settings.

In a further embodiment of the foregoing aircraft controller, thenon-transient storage medium further stores instructions for causing thecontroller to perform the step of determining the aircraft controlsurface setting in the cruise flight mode of operations by determining arunning average of the aircraft control surface setting in the cruiseflight mode over at least a portion of the cruise flight mode ofoperations.

In a further embodiment of the foregoing aircraft controller, thenon-transient storage medium further stores instructions for causing thecontroller to perform the step of determining the aircraft controlsurface setting in the cruise flight mode of operations by determiningan instantaneous aircraft control surface setting as the aircraft exitsthe cruise mode of operations and enters a pre-landing procedure.

In a further embodiment of the foregoing aircraft controller, thenon-transient storage medium further stores instructions for causing thecontroller to perform the step of determining the aircraft controlsurface setting in the flight idle mode of operations by determining aninstantaneous aircraft control surface setting as the aircraft entersthe flight idle mode of operations.

In a further embodiment of the foregoing aircraft controller, theaircraft control surface setting is an aircraft control surfacedeflection.

In a further embodiment of the foregoing aircraft controller, theaircraft control surface is a rudder.

In a further embodiment of the foregoing aircraft controller, the stepof comparing the aircraft control surface setting in the cruise flightmode with the aircraft control surface setting in the flight idle modeof operations further includes subtracting a variable dependent on theaircraft control surface setting in the flight idle mode of operationsfrom the aircraft control surface setting in the cruise flight mode.

In a further embodiment of the foregoing aircraft controller, the stepof determining an asymmetric thrust bias based on the isolatedasymmetric thrust component of the aircraft surface settings furtherincludes determining a thrust differential between a plurality ofengines on a multi-engine aircraft required to necessitate theasymmetric thrust component of the aircraft surface settings.

An aircraft controller according to an embodiment of this disclosure,among other possible things includes a non-transient storage medium, thenon-transient storage medium storing instructions operable to cause thecontroller to perform the step of applying at least one asymmetricthrust bias determined in a previous flight to a thrust balancing systemof a multi-engine aircraft, thereby accounting for engine discrepancies.

In a further embodiment of the foregoing aircraft controller, thenon-transient storage medium further stores instructions for causing thecontroller to perform the step of determining an average asymmetricthrust bias of a plurality of previous flights and the step of applyingat least one asymmetric thrust bias determined in a previous flight to athrust balancing system of the multi-engine aircraft comprises applyingthe average asymmetric thrust bias.

In a further embodiment of the foregoing aircraft controller, theaverage asymmetric thrust bias is a weighted average, thereby accountingfor anomalous flight conditions.

In a further embodiment of the foregoing aircraft controller, thenon-transient storage medium further stores instructions for causing thecontroller to perform the step of disabling a thrust balancing systemduring at least one of landing procedures and take off procedures.

In a further embodiment of the foregoing aircraft controller, the stepof applying at least one asymmetric thrust bias determined in a previousflight to a thrust balancing system of the multi-engine aircraft,thereby accounting for engine discrepancies is performed during at leastone of pre-flight procedures, take off, and transition to a cruise modeof operations.

In a further embodiment of the foregoing aircraft controller, thenon-transient storage medium stores instructions for causing thecontroller to perform the step of determining a thrust metric of each ofthe engines on the multi-engine aircraft, applying a thrust balancingvalue based on the asymmetric thrust bias to the thrust metric of atleast one of the engines, thereby generating an adjusted thrust metricaccounting for engine discrepancies, and adjusting a thrust of at leastone of the engines based on the adjusted thrust metric. As is understoodin the art, the thrust produced by an aircraft engine is controlled viaan aircraft controller. The output signal of the aircraft controllerutilized to control the amount of thrust produced by a given engine isreferred to herein as a “thrust output control signal”.

In a further embodiment of the foregoing aircraft controller, the thrustmetric is at least one of an engine pressure ratio (EPR) and a low rotorfan speed (N1).

A multi-engine aircraft according to an exemplary embodiment of thisdisclosure, among other possible things includes a plurality of engines,at least one of the engines mounted to a first wing of the aircraft andat least one of the engines mounted to a second wing of the aircraft, anaircraft control surface operable to adjust a heading of the aircraft,and an aircraft controller operable to control a deflection of theaircraft control surface, the aircraft controller including a memorystoring instructions for causing the aircraft controller to perform athrust balancing method including the steps of comparing an aircraftcontrol surface setting in a cruise flight mode with the aircraftcontrol surface setting in a flight idle mode of operations, therebyisolating an asymmetric thrust component of the aircraft surfacesettings, and determining an asymmetric thrust bias based on theisolated asymmetric thrust component of the aircraft surface settings.

In a further embodiment of the foregoing multi-engine aircraft, theaircraft control surface is an aircraft rudder.

In a further embodiment of the foregoing multi-engine aircraft, includesa sensor located at the aircraft control surface and connected to theaircraft controller, such that the sensor can transmit the aircraftcontrol surface deflection to the aircraft controller.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example multi-engine aircraft with symmetricalengine thrusts.

FIG. 2 illustrates an example multi-engine aircraft with asymmetricalengine thrusts.

FIG. 3 illustrates a flowchart of a method for determining an asymmetricthrust bias of a multi-engine aircraft.

FIG. 4 illustrates a flowchart of a thrust balancing method for amulti-engine craft.

DETAILED DESCRIPTION OF AN EMBODIMENT

FIG. 1 schematically illustrates a multi-engine aircraft 10 including afirst turbine engine 20 and a second turbine engine 30. The aircraftincludes a control surface 40, such as a rudder, that maintains aheading 60 of the aircraft 10 during flight. Each of the engines 20, 30outputs a certain amount of thrust 22, 32 which propels the aircraftforward and cooperates with the wing design to generate lift, liftingthe aircraft. A controller 50 is connected to each of the engines 20, 30via engine control lines 52, 54 and to the aircraft control surface 40via a control surface control line 56. The controller 50 includes anon-transient memory for storing control instructions. The aircraft 10also includes a flight deck computer 51 that is connected to thecontroller 50, and is operable to provide heading information and otherflight information from the flight deck 51 to the controller 50.

During standard flight conditions the balanced thrust 22, 32 produced bythe engines 20, 30 maintains the aircraft heading 60 in a forwarddirection while requiring minimal actuation of the aircraft controlsurface 40. The engine thrusts are typically balanced using either ameasured engine pressure ratio (EPR) or a measured low rotor fan speed(N1) to approximate the thrust generated by the engines. EPR and N1 arereferred to in the art as “thrust metrics”.

When the thrust metrics of each engine 20, 30 are the same, it isgenerally assumed that the output thrust 22, 32 is approximately thesame between the two engines 20, 30. It is known in the art that thecurrently used thrust metrics do not reflect the actual thrust produced,but provide an approximation of the thrust produced. In identicalengines 20, 30, an identical thrust metric will generate identicalthrust.

On multi-engine aircraft, such as the aircraft 10 illustrated in FIG. 1,often at least one older engine 30 and one newer engine 20 are includedon the aircraft for safety purposes. As a result of the different agesand wear on the engines 20, 30, the existing thrust metrics (EPR, N1) donot result in identical thrusts with identical thrust metric values inthe practical implementation.

With continued reference to FIG. 1 and with like numerals indicatinglike elements, FIG. 2 illustrates an example multi-engine aircraft 10including a newer engine 20 and an older engine 30. The older engine 30includes more wear on the engine components, and produces a smalleramount of thrust 32 than the newer engine 20 at the same thrust metricas a result of the wear. The difference between the thrust produced oneach side of the aircraft 10 is referred to as asymmetric thrust. Inalternate examples the older engine 30 may produce a larger amount ofthrust at the same thrust metric.

As a result of the asymmetric thrust, the engine control surface 40 isdeflected in order to maintain the aircraft 10 on the correct heading60. The deflection introduces, additional drag on the aircraft and thefuel efficiency of the aircraft 10 is negatively impacted. A typicalaircraft flight spends over 80% of the engine operation time in cruiseoperations, where the fuel efficiency loss is notable, and correctible.

At the end of the flight, as the aircraft 10 begins its pre-landingprocedures, the aircraft 10 enters a flight idle operations mode. Duringthe flight idle operations mode, the thrust produced by the engines isreduced to a relatively low amount compared with other modes ofoperations during the flight. As the aircraft transitions into theflight idle mode of operations, the controller 50 measures the change insettings of the aircraft control surface 40 required to maintain theaircraft on its proper heading 60. The settings (amount of deflection)of the aircraft control surface 40 in flight idle mode approximate thesettings required to maintain the heading 60 as a result ofenvironmental factors not including the thrusts 22, 32 produced by theengines 20, 30. By way of example, the environmental factors can be awind direction, a wind speed, turbulence levels, etc. that vary as theaircraft changes altitude levels.

By comparing the settings of the aircraft control surface 40 in flightidle mode against the settings of the aircraft control surface 40 incruise mode, the amount of aircraft control surface 40 deflectionrequired to compensate for the thrust differences of the aircraftengines 20, 30 can be determined. In some examples, the headinginformation provided by an aircraft flight controller is included in thecomparison, thereby accounting for a turn immediately prior to, orduring, a landing procedure. This value is referred to as an asymmetricthrust bias. This determination is then used by an on-board computer,controller (such as the controller 50), or any other computerizedaircraft component to determine asymmetric thrust values of the engines20, 30 and provide corrected thrust settings in future aircraft flights,thereby recognizing an increase in fuel efficiency. In examples wherethe heading information indicates a significant turn, the flight datamay be invalidated within the controller due to the crosswind change asa result of the heading change.

FIG. 3 illustrates a method 200 for determining an asymmetric thrustbias of a multi-engine aircraft utilizing the above described feature.Initially, at Step 210, during the standard cruise engine operations ofan aircraft flight, a controller 50 or other computerized aircraftcomponent determines the deflection of an aircraft control surface suchas an aircraft rudder. In one example this determination is madeimmediately before the aircraft exits the cruise mode of operations andenters flight idle operations. This transition occurs typically duringpre-landing procedures, however it is understood that the transition canoccur at other points during a flight as well. In alternate examples,the determination can be made at other points during the cruise mode ofoperations or as a running average over the duration of the engine'scruise mode.

Then, at Step 220, when the aircraft engines enter a flight idle mode ofoperations, the controller 50 or other computerized aircraft componentagain determines the aircraft control surface deflection. In someexamples, the aircraft control surface deflection is measured once theaircraft has fully entered the flight idle mode. In alternate examples,the aircraft control surface deflection is measured over time as theaircraft enters the flight idle mode, and the change in aircraft controlsurface deflection indicates what the flight idle aircraft controlsurface deflection will be.

In the case of both the previously described steps 210, 220, theaircraft control surface deflection can be determined either based onthe control outputs generated by the controller 50 and passed to theaircraft control surface or by an additional sensor located at theaircraft control surface and operable to measure the deflection of theaircraft control surface. Alternately, other known methods ofdetermining the aircraft control surface deflection can be utilized tothe same effect.

Then, at Step 230, when both the flight idle and the cruise modeaircraft control surface deflection are determined, the controller 50 orother computerized aircraft component compares the determined aircraftcontrol surface deflections relative to each other and isolates acomponent of the control surface deflection during cruise modeoperations that is the result of asymmetric engine thrusts. In someexamples, this isolation is done by subtracting a variable dependentupon the surface deflection at flight idle mode from the surfacedeflection in the cruise operations mode, and the asymmetric thrustdeflection is the remainder.

Then, at Step 240, once the amount of surface deflection of the aircraftcontrol surface is determined, the computerized control system utilizesthe asymmetric thrust component of the control surface deflection todetermine an asymmetric thrust bias of each of the engines. Theasymmetric thrust bias of the engines represents the actual amount ofthrust produced by each engine relative to the actual thrust produced bythe other engines at a near identical thrust metric such as EPR or N1.

As the flight idle mode of operations is typically entered into as theaircraft prepares to enter landing procedures, the cruise portion of theflight is typically over before the asymmetric thrust bias is determinedfor a particular flight. Thus, the asymmetric thrust bias is stored inan aircraft memory, and applied in future flights. In this way also, theaircraft 10 can update the aircraft thrust bias after each flight, andmaintain a more accurate engine balancing system than existing thrustbalancing systems.

Once the asymmetric thrust bias of the engines for a particular flighthas been determined, the aircraft 10 can utilize the asymmetric thrustbias to correct for the asymmetric thrust during future cruiseoperations.

FIG. 4 illustrates a method 300 of utilizing previously determinedasymmetric thrust data to balance engine thrusts 22, 32 on amulti-engine aircraft 10. At Step 310, at the beginning of a flight, orduring pre-flight procedures, the controller 50 or another computerizedaircraft component initially recalls stored asymmetric thrust data fromprevious flights. In some example systems, the controller 50 onlyrecalls the asymmetric thrust bias data from the most recent previousflight. In alternate example systems, the controller 50 can recallstored asymmetric thrust bias data from multiple previous flights, andutilize a running average of the asymmetric thrust bias data or aweighted average of the asymmetric thrust bias data.

In one example, the running average is a flat mean average of theasymmetric thrust bias data for a set number of immediately priorflights. Utilizing the running average allows the controller 50 tominimize the impact of anomalous environmental conditions or engineconditions, while still providing an improved thrust balancing system.

Similarly, in one example the weighted average is a mean average of theasymmetric thrust bias data for a set number of immediately priorflights, with a weighting value applied to each flight. In this way acontroller 50 can account for particularly strong cross winds during thetransition to flight idle operations by giving a particular flight'sasymmetric thrust bias data a low weight, such as 0.1. Similarly, thecontroller 50 can account for particularly weak cross winds by assigninga high weight, such as 1.9, to a particular flight's asymmetric thrustbias data when the flight had particularly low cross winds during thetransition to flight idle operations. In this way the controller 50 canactively account for particularly anomalous situations. The weightingvalue is a multiplicative value applied to the asymmetric thrust biasdata and increases or decreases the weight of a particular flight's datawithin a set of multiple of flights.

In yet another alternate example of the process of FIG. 4, thecontroller 50 can discard asymmetric thrust bias data from a flight whenthat flight is too anomalous. The discarding of the data can either bethrough an automated process, based on flight conditions detected by theaircraft systems, or a manual system where an employee, aircrafttechnician, or ground based computer system manually removes theanomalous flight data.

At Step 320, once the stored asymmetric thrust biases are recalled, thecontroller 50 determines the appropriate asymmetric thrust bias offsetsettings. That is, during this step, the controller 50 determines anactual bias offset value to apply to each engine. The bias offset valueoffsets the thrust metrics (EPR or N1) seen by the controller 50 toaccount for the bias determined in the previous flights. The bias offsetvalues are determined for each engine relative to each other engine onthe aircraft.

Once the bias offset value for each engine has been determined, the biasoffset value is stored for later use. Then, at Step 330, when theaircraft 10 enters the cruise mode of operations, the controller 50applies the bias offset values determined in Step 320 to the aircraftengine controls. By applying the thrust bias offsets to the enginecontrols, the controller 50 offsets the detected thrust metric of atleast one of the engines 20, 30 being used to balance the enginethrusts, and generate symmetric thrust from the engine, therebyminimizing the aircraft control surface deflection required to maintaina heading, and increasing the fuel efficiency of the aircraft duringcruise operations.

While the method 300 of utilizing previously determined asymmetricthrust data to balance engine thrusts 22, 32 is described above as beinginitiated at the beginning of a flight, it is further understood thatthe method 300 could alternately be performed once the aircraft 10reaches cruise altitude, or by the aircraft 10 during its ascent.

Furthermore, while the above describe method is described generally withregards to a twin engine aircraft 10, such as the aircraft illustratedin FIGS. 1 and 2, it is understood that the methods and devicesdescribed herein can be applied to multi-engine aircraft including anynumber of engines on each side of the aircraft.

In yet another example, the asymmetric thrust biasing system can besuspended or switched off at step 340 during takeoff and landingprocedure in order to provide enhanced control to the pilot. Theasymmetric thrust balancing system can similarly be suspended orswitched off at step 340 during any operation in which enhanced pilotcontrol is desired.

It is further understood that any of the above described concepts can beused alone or in combination with any or all of the other abovedescribed concepts. Although an embodiment of this invention has beendisclosed, a worker of ordinary skill in this art would recognize thatcertain modifications would come within the scope of this invention. Forthat reason, the following claims should be studied to determine thetrue scope and content of this invention.

The invention claimed is:
 1. An aircraft controller comprising: anon-transient storage medium, the non-transient storage medium storinginstructions operable to cause the controller to perform the steps of:determining a setting of an aircraft control surface while in a flightidle mode of operations by determining an instantaneous setting of theaircraft control surface as the aircraft enters the flight idle mode ofoperations; comparing a setting of the aircraft control surface while ina cruise flight mode of the aircraft with the setting of the aircraftcontrol surface while in the flight idle mode of operations of theaircraft, thereby isolating an asymmetric thrust component of thesettings of the aircraft control surface; determining an asymmetricthrust bias based on the isolated asymmetric thrust component of thesettings of the aircraft control surface; and adjusting a thrust outputcontrol signal, thereby compensating for the determined asymmetricthrust bias.
 2. The aircraft controller of claim 1, wherein thenon-transient storage medium further stores instructions for causing thecontroller to perform the step of determining the setting of theaircraft control surface while in the cruise flight mode of operationsby determining a running average of the setting of the aircraft controlsurface while in the cruise flight mode over at least a portion of thecruise flight mode of operations.
 3. The aircraft controller of claim 1,wherein the non-transient storage medium further stores instructions forcausing the controller to perform the step of determining the setting ofthe aircraft control surface while in the cruise flight mode ofoperations by determining an instantaneous setting of the aircraftcontrol surface as the aircraft exits the cruise mode of operations andenters a pre-landing procedure.
 4. The aircraft controller of claim 1,wherein the setting of the aircraft control surface is an aircraftcontrol surface deflection.
 5. The aircraft controller of claim 1,wherein the aircraft control surface is a rudder.
 6. The aircraftcontroller of claim 1, wherein the step of comparing the setting of theaircraft control surface while in the cruise flight mode with thesetting of the aircraft control surface while in the flight idle mode ofoperations further comprises subtracting a variable dependent upon thesetting of the aircraft control surface while in the flight idle mode ofoperations from the setting of the aircraft control surface while in thecruise flight mode.
 7. The aircraft controller of claim 1, wherein thestep of determining an asymmetric thrust bias based on the isolatedasymmetric thrust component of the settings of the aircraft controlsurface further comprises determining a thrust differential between aplurality of engines on a multi-engine aircraft required to necessitatethe asymmetric thrust component of the settings of the aircraft controlsurface.
 8. A multi-engine aircraft comprising: a plurality of engines,at least one of the engines mounted to a first wing of the aircraft andat least one of the engines mounted to a second wing of the aircraft; anaircraft control surface operable to adjust a heading of the aircraft;and an aircraft controller operable to control a deflection of theaircraft control surface, the aircraft controller including a memorystoring instructions for causing the aircraft controller to perform athrust balancing method including the steps of: determining a flightidle mode setting of the aircraft control surface while in the flightidle mode of operations by determining an instantaneous setting of theaircraft control surface as the aircraft enters the flight idle mode ofoperations; determining a cruise mode setting of the aircraft controlsurface while the aircraft is in the cruise mode of operations;comparing the cruise mode setting of the aircraft control surface withthe flight idle mode setting of the aircraft control surface, therebyisolating an asymmetric thrust component of the settings of the aircraftcontrol surface; and determining an asymmetric thrust bias based on theisolated asymmetric thrust component of the settings of the aircraftcontrol surface.
 9. The multi-engine aircraft of claim 8, wherein theaircraft control surface is an aircraft rudder.
 10. The multi-engineaircraft of claim 8, further comprising a sensor located at the aircraftcontrol surface and connected to the aircraft controller, such that thesensor can transmit the aircraft control surface deflection to theaircraft controller.